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1.
《Aquacultural Engineering》2010,42(3):188-193
The removal of phytoplankton cells from aquaculture systems generally results in the reduction of nitrogenous waste and improves water quality. With this study, the effects of chitosan concentration, environmental condition and pH adjustment on flocculation of phytoplankton in marine shrimp (Litopenaeus vannamei) culture tanks were investigated. The remaining phytoplankton and suspended solids in the system were indicators for evaluating the efficiency of chitosan on flocculation. The results indicate that the flocculation efficiency of chitosan was highest (>85%) and remained fairly constant at a chitosan concentration of 40–80 mg L−1 and a pH range of 7–9 after chitosan addition. With this novel technique including 40 mg L−1 chitosan addition, pH adjustment to 6.5 and then to 8.5, high efficiency and consistency of flocculation were achieved. This technique could also be applied with various water alkalinity up to 400 mg CaCO3 L−1. The experiment for phytoplankton removal by chitosan flocculation in the recirculating aquaculture system showed that flocculation efficiency remained constant even though flocculation was repeated several times.  相似文献   

2.
The removal of phytoplankton cells from aquaculture systems generally results in the reduction of nitrogenous waste and improves water quality. With this study, the effects of chitosan concentration, environmental condition and pH adjustment on flocculation of phytoplankton in marine shrimp (Litopenaeus vannamei) culture tanks were investigated. The remaining phytoplankton and suspended solids in the system were indicators for evaluating the efficiency of chitosan on flocculation. The results indicate that the flocculation efficiency of chitosan was highest (>85%) and remained fairly constant at a chitosan concentration of 40–80 mg L?1 and a pH range of 7–9 after chitosan addition. With this novel technique including 40 mg L?1 chitosan addition, pH adjustment to 6.5 and then to 8.5, high efficiency and consistency of flocculation were achieved. This technique could also be applied with various water alkalinity up to 400 mg CaCO3 L?1. The experiment for phytoplankton removal by chitosan flocculation in the recirculating aquaculture system showed that flocculation efficiency remained constant even though flocculation was repeated several times.  相似文献   

3.
In zero-exchange superintensive culture systems, flocculated particles (bioflocs) accumulate in the water column. Consequently, some control over the concentration of these particles must be performed. The objective of this study is to evaluate the effects of three concentrations of bioflocs on microbial activity, selected water quality indicators and performance of Litopenaeus vannamei in a tank system operated with no water exchange. A 44-day study was conducted with juvenile (6.8 g) shrimp stocked in twelve 850 L tanks at a stocking density of 459 shrimp m−3. Biofloc levels were expressed as three presets of total suspended solids (TSS) concentrations, as follows: 200 mg L−1 (T200), 400–600 mg L−1 (T400–600), and 800–1000 mg L−1 (T800–1000). TSS levels were controlled by attaching a 40 L settling tank to each culture tank. Reduction of TSS to concentrations close to 200 mg L−1 decreased the time of bacterial cell residence and significantly reduced the nitrification rates in the water (P < 0.05). The tanks in the T200 treatment had a greater variability of ammonia and nitrite (P < 0.05), which led to the need to increase the C:N ratio of the organic substrate to control ammonia through its assimilation into heterotrophic bacterial biomass. But the higher production of heterotrophic bacteria in T200 (P < 0.05) increased the dissolved oxygen demand. Nitrification rates were higher (P < 0.05) in tanks with TSS concentrations above 400 mg L−1, and ammonia and nitrite were significantly lower than in the T200 tanks. We suggest that ammonia and nitrite in the T400–600 and T800–1000 tanks were controlled primarily by nitrifying bacteria, which provided higher stability of these parameters and of dissolved oxygen. Regarding shrimp performance, the reduction of TSS to levels close to 200 mg L−1 was associated with better nutritional quality of bioflocs. Nevertheless, differences in biofloc levels and nutritional quality were not sufficient to affect the weight gain by shrimp. The rate of shrimp survival and the final shrimp biomass were lower (P < 0.05) when the TSS concentrations were higher than 800 mg L−1. Analysis of the shrimps’ gills showed a higher degree of occlusion in the T800–1000 treatment (P < 0.05), which suggests that the shrimp have an intolerance to environments with a solids concentration above 800 mg L−1. Our results show that intermediate levels of bioflocs (TSS between 400 and 600 mg L−1) appear to be more suitable to superintensive culture of L. vannamei since they create factors propitious for maintaining the system’s productivity and stability  相似文献   

4.
The removal of Tricaine Methanesulfonate from water in a fixed-bed column packed with pyrolysed paper mill sludge was evaluated for application in Recirculating Aquaculture Systems. Breakthrough adsorption curves were determined for this pharmaceutical, under different operating conditions. In a laboratory-scale approach, with synthetic effluent, a bed adsorption capacity of 125 mg g−1 was obtained under a flux of 56 L min−1 m−2, with 400 mg L−1 of MS-222 with 4.5 cm bed depth. The performance of the continuous adsorption in a column packed with biological paper mill sludge-based carbon, using real aquaculture wastewater as matrix, was not significantly affected. Then, scale-up was carried out and the bed depth service time model was applied and provided good predictions. Finally, the thermal regeneration of the exhausted adsorbent was assessed, which revealed satisfactory results for one cycle reusability after saturation; however, considering the nature of its precursor, the use of new adsorbent could be more profitable than its regeneration, functioning also as an additional option for the management of such wastes.  相似文献   

5.
A study was undertaken to measure the water flow (Qw) delivered by a vacuum airlift designed for recirculating aquaculture systems (RAS) in fresh (<1‰ of salinity) and sea water (35‰ of salinity). The vacuum airlift consists of two concentric tubes connected at their top to a depression chamber. The water rises in the inner tube as a result of air being injected in its lower section and flows back through the external downcomer tube. The vacuum airlift was adjusted at three different lengths: 2, 4 or 6 m and water discharge could be lifted from 0 to 30 cm. Air flow rate (Qg) varied from 0 to 80 L min−1. Different types of air injectors were tested, delivering different bubble sizes (0.1–5 mm) depending on porosity and functioning at low or high injection pressure. Results show an increase in water flow when pipe length and air flow were increased and lift height reduced. Water flow also depended on the type of water and ranged from 0 to 35 m3 h−1 (0–580 L min−1) for fresh water and only from 0 to 20 m3 h−1 (0–330 L min−1) for sea water (for a 6 m high vacuum airlift). This difference was attributed to the smaller bubble diameter and higher gas holdup (ɛg) observed in sea water (0–20%) compared to fresh water (0–10%). When bubbles were present in the downcomer tube, they created a resistance to flow (counter-current airlift) that slowed down liquid velocity and thus water flow. Increasing the vacuum made it possible to use low air injection pressures and high injection depths. Vacuum also increased bubble size and airflow (20 L min−1 at atmospheric pressure to 60 L min−1 at 0.3 barA) and thus water flow rates. With RAS, the presence of fish feed in water rapidly increased water flow delivered by the airlift because of changes of water quality and gas holdup. When working with low head RAS (under 0.3 m), vacuum airlift could save up to 50% of the energy required for centrifugal pumps. An empirical predictive model was developed and calibrated. Simulation shows a good correlation between predicted values and measurements (R2 = 0.96).  相似文献   

6.
A 13-day nursery trial was conducted to evaluate the performance of young Litopenaeus vannamei post-larvae (from PL6 to PL18) reared in both biofloc and microalgae-based systems at a stocking density of 67 PLs L−1. The effects of different concentrations of total suspended solids (TSS) on PL performance were also evaluated. One experimental group was reared in a conventional microalgae-based system with daily water exchange and daily addition of microalgae (herein called microalgae treatment). The other two experimental groups were reared using biofloc technology (BFT) with daily dextrose addition and no water exchange, but in the “Biofloc-500” treatment, TSS were maintained at around 500 mg L−1, while in the “Biofloc-700” treatment, TSS were maintained at around 700 mg L−1. Water quality variables remained within the appropriate range for larval culture. In microalgae treatment, ammonia control was likely associated with its assimilation into microalgae biomass and daily water exchange. In biofloc tanks, however, the addition of dextrose stimulated the production of bacterial biomass from ammonia. This system required only 12.9% of the water used by the microalgae treatment since water was not exchanged during the culture. The nursery of young PLs resulted in similar (P > 0.05) performance in all treatments: survival >94%, PL length ∼ 11.5 mm, and PL dry weight ∼ 1.2 mg. In addition, the salinity stress test (>90.0%) was not significantly different among treatments. Our results indicate that BFT can be as effective as the microalgae-based system for the nursery of young L. vannamei post-larvae. We also found that post-larvae performance was similar (P > 0.05) between biofloc treatments, indicating that organisms can tolerate environments with large quantities of solids.  相似文献   

7.
Decreased Litopenaeus vannamei performance resulting from excess total suspended solids (TSS) has been highlighted in previous studies. Therefore, the aim of this study was to evaluate the effect of different TSS concentrations on the L. vannamei growth performance in a BFT system for 42 days. Five TSS concentrations were used—250, 500, 1000, 2000, and 4000 mg L−1—in three replicates identified as T250, T500, T1000, T2000, and T4000, respectively, in 200 L-tanks each. Dissolved oxygen concentration (DO) was maintained above 5 mg L−1. Shrimp with an initial average weight of 4.57 ± 1.07 g were stocked at a density of 277 shrimp m−2. The physical and chemical parameters were monitored. Water quality parameters and animal performance were subjected to analysis of variance (ANOVA − one way). The physical and chemical parameters were within the recommended range for L. vannamei. Weekly weight gain, feed conversion rate, survival, and productivity showed no significant differences (p > 0.05). The high TSS concentrations did not seem to affect the performance of this species when DO concentrations were maintained above 5 mg L−1.  相似文献   

8.
A new physico-chemical process for ammonia removal from fresh-water recirculated aquaculture systems (RASs) is introduced. The method is based on separating NH4+ from RAS water through an ion-exchange resin, which is subsequently regenerated by simultaneous chemical desorption and indirect electrochemical ammonia oxidation. Approach advantages include (1) only slight temperature dependence and no dependence on bacterial predators and chemical toxins; (2) no startup period is required and the system can be switched on and off at will; and (3) the fish are grown in much lower bacterial concentration, making the potential for both disease and off-flavor, lower. A small pilot scale RAS was operated for 51 d for proving the concept. The system was stocked by 105 tilapia fish (initial weight 35.8 g). The fish, which were maintained at high TAN (total ammonia nitrogen) concentrations (10–23 mgN L−1) and fish density of up to 20 kg m−3, grew at a rate identical to their established growth potential. NH3(aq) concentrations in the fish tank were maintained lower than the assumed toxicity threshold (0.1 mgN L−1) by operating the pond water at low pH (6.5–6.7). The low pH resulted in efficient CO2 air stripping, and low resultant CO2(aq) concentrations (<7 mg L−1). Due to efficient solids removal, no nitrification was observed in the fish tank and measured nitrite and nitrate concentrations were very low. The system was operated successfully, first at 10% and then at 5% daily makeup water exchange rate. The normalized operational costs, calculated based on data derived from the pilot operation, amounted to 28.7 $ cent per kg fish feed. The volume of the proposed process was calculated to be ∼13 times smaller than that of a typical RAS biofilter. The results show the process to be highly feasible from both the operational and economical standpoints.  相似文献   

9.
Total suspended solids are a priority pollutant under the Clean Water Act and a point of concern for aquaculture facilities. The use of ubiquitous vegetated ditches on the aquaculture landscape may serve as an environmentally and economically sustainable practice for reducing suspended sediment contributions to downstream environments. This study assessed effects of consecutive low-grade weirs on suspended solids retention and settling rates of aquaculture pond effluent in a single drainage ditch. Two control and nine treatment discharges were conducted in September and October 2012 at the Mississippi State University South Farm Aquaculture Facility. All discharges decreased total and volatile suspended solid loads. Total suspended solids were decreased 72–94%, with a significant removal rate of 0.02 ± 0.01 mg L−1 min−1 in both control (F = 6.12, P < 0.001) and treatment discharges (F = 16.02, P < 0.001). Volatile suspended solids comprised 2–80% of total suspended solids and had a significant removal rate of 0.02 ± 0.001 mg L−1 min−1 in both control (F = 10.46, P < 0.001) and treatment discharges (F = 6.28, P < 0.001). There was no significant difference in overall settling rates between control and treatment discharges; however, prior to weir 1, both total and volatile suspended solid concentrations increased in control discharges. Treatment discharges decreased both total and volatile suspended solids significantly (P < 0.001) prior to weir 1. Further analysis revealed flow rate to be a significant (P < 0.001) variable in total suspended solid removal while initial concentrations affected reduction rates of volatile suspended solids significantly (P < 0.001). These results suggest that the use of low-grade weirs could be a viable best management practice that easily integrates within the aquaculture landscape and creates hydraulic conditions conducive to sediment retention.  相似文献   

10.
Peracetic acid (PAA) products are being introduced to aquaculture as sustainable disinfectants. Two strategies are used to apply PAA: high dose pulse applications, or low dose continuous application. In the present study, their impacts on fish health and water quality were investigated in triplicate flow-through tanks stocked with rainbow trout. The gentler and shorter water cortisol increase measured along twice-per-week pulse applications of 1 mg L−1 PAA indicated a progressive adaptation of fish. In contrast, the continuous application of 0.2 mg L−1 PAA caused no stress to fish. Meanwhile, no mortality and no impact on growth or innate cellular immunity were observed. The pulse applications restricted biofilm formation, and partially inhibited nitrification. Additionally, the highest oxygen concentration and stable pH were observed. In contrast, the continuous application promoted biofilm formation, and caused a pH increase and intermediate oxygen concentration. The contrast was probably due to different susceptibility of microbes to PAA-induced oxidative stress. To summarize, pulse PAA applications cause minor stress in fish, but have advantages over continuous application by ensuring better water quality.  相似文献   

11.
A 56-day study was conducted in which shrimp (Litopenaeus vannamei) were stocked at 300 m−3 into 16, 500-L tanks. Four treatments were created: chemoautotrophic (CA), heterotrophic sucrose (HS), heterotrophic molasses (HM), and heterotrophic glycerol (HG). The heterotrophic treatments were managed such that the C:N ratio of inputs (feed and carbohydrate source) was 22:1. The chemoautotrophic treatment received no added carbohydrate, only shrimp feed. Each treatment was assigned randomly to four replicate tanks. Nitrate-N was significantly greater in the CA treatment, accumulating to a peak mean concentration of 162 mg NO3-N L−1 and nitrate was typically below detection (<0.01 mg NO3-N L−1) in the heterotrophic treatments. 5-Day biochemical oxygen demand (BOD5) was significantly greater in the heterotrophic treatments compared to the chemoautotrophic treatment. Total suspended solids concentration was significantly lower in the CA treatment compared to any other. Shrimp growth rate was significantly greater in the CA and HS treatments versus the HM treatment and there was no significant difference in growth rate between the HG treatment and any other treatment. These results indicate that differences in management and carbohydrate source can lead to substantial disparity in system function and shrimp production.  相似文献   

12.
Denitrification reactors have proven their functionality in commercial recirculation aquaculture systems (RAS). Nevertheless, clogging occurs due to the low hydraulic loads necessary to accomplish anoxic conditions for a successful denitrification process in RAS, which hampers the adjustment of stable working conditions within fixed bed denitrification reactors. Reactors working on the basis of activated sludge demand careful hydraulic control and/or complex configurations for sludge retention.To develop a low-maintenance denitrification reactor, an enclosed moving bed filter, driven by recirculation of the inherent, oxygen poor gas was designed. A Self cleaning Inherent gas Denitrification reactor (SID-reactor) of 0.65 m3, which offered a moving bed volume of 0.39 m3 was connected with a RAS of semi-industrial scale for pike perch (Sander lucioperca) production. This species indicates suboptimal environmental conditions (as e.g. NO3-N concentrations above approximately 68 mg l−1) by prompt reduction of the feed intake. In different experimental series, the SID-reactor was operated with denatured ethanol, methanol, acetic acid or glycerin as carbon sources and changing operational modes.Clogging was prevented by a 40 second inherent gas recirculation twice an hour, which provided continuous, maintenance free operation with marginal energy demand. With inlet (RAS) and outlet NO3-N concentrations in the range of 49 mg l−1 and 12 mg l−1, mean denitrification rates of 199 g to 235 g NO3-N per m3 moving bed volume and day were determined for all tested carbon sources. Negative effects on the feed intake of the reared pike perch were detected with all carbon sources except methanol. Changing the mode of operation to continuous circulation of the filter bed at inlet NO3-N concentrations of 26 mg l−1, the denitrification performance reached 451 g NO3-N per m3 moving bed volume and day. The SID-reactor allowed for the reduction of freshwater exchange in the pike perch RAS from 600 l to 70 l (−88%) and the sodium bicarbonate buffer from 182 g to 31 g (−83%) per kg of administered food. The easy and reliable operation of the SID-reactor could help to establish controlled denitrification as a routine purification step in RAS.  相似文献   

13.
《Fisheries Research》2007,83(1-3):74-86
The life history of an increasingly important pelagic commercial and sport fish, the Talang queenfish, Scomberoides commersonnianus, was studied in northern Australia to investigate the stock status and assess current management of the species using minimum legal lengths (MLL). Estimated von Bertalanffy growth parameters were L∞ = 1404 mm FL, K = 0.10 year−1 and t0 = −1.21 year−1. There was no significant difference in growth between sexes. Ages ranged from 1 to 11 years with age composition differing between the commercial (mainly 6–7 years) and sport fishery (mainly 2–4 years). Females matured (L50) at 635 mm FL and 4–5 years. Spawning occurred between August and March when mature females were estimated to produce 259,488–2,859,935 eggs per spawning. Natural mortality (M) was estimated as 0.16–0.26 year−1, while the combined fishing mortality (Fcurrent) from commercial and sport fisheries was 0.38–0.48 year−1. Yield-per-recruit analyses revealed that under current MLL limits (no MLL or 45 cm TL) and natural mortality (M = 0.16, 0.2 and 0.26 year−1), Fcurrent exceeded the reference points Fmax (0.15–0.22 year−1) and F0.1 (0.10–0.15 year−1), suggesting the stock may be growth overfished if the current situation remains unchanged. Although a stock–recruitment relationship is unknown, spawning stock biomass-per-recruit analysis indicates the stock may also be recruitment overfished since Fcurrent exceeded the reference points F25% (0.19–0.24 year−1) and F40% (0.11–0.15 year−1). Increasing the MLL corresponding to L50 of females (70 cm TL) will greatly improve the yield and long-term sustainability of the stock, and also enhance the sport fishery by increasing the number of larger trophy fish.  相似文献   

14.
A step toward environmental sustainability of recirculat aquaculture systems (RAS) is implementation of single-sludge denitrification, a process eliminating nitrate from the aqueous environment while reducing the organic matter discharge simultaneously. Two 1700 L pilot-scale RAS systems each with a 85 L denitrification (DN) reactor treating discharged water and hydrolyzed solid waste were setup to test the kinetics of nitrate and COD removal. Nitrate removal and COD reduction efficiency was measured at two different DN-reactor sludge ages (high θX: 33–42 days and low θX: 17–23 days). Nitrate and total N (NO3− + NO2− + NH4+) removal of the treated effluent water ranged from 73–99% and 60–95% during the periods, respectively, corresponding to an overall maximum RAS nitrate removal of approximately 75%. The specific nitrate removal rate increased from 17 to 23 mg NO3−-N (g TVS d)−1 and the maximal potential DN rate (measured at laboratory ideal conditions) increased correspondingly from 64–68 mg NO3−-N (g TVS d)−1 to 247–294 mg NO3−-N (g TVS d)−1 at high and low θX, respectively. Quantification of denitrifiers in the DN-reactors by qPCR showed only minor differences upon the altered sludge removal practice. The hydrolysis unit improved the biodegradability of the solid waste by increasing volatile fatty acid COD content 74–76%. COD reductions in the DN-reactors were 64–70%. In conclusion, this study showed that single-sludge denitrification was a feasible way to reduce nitrate discharge from RAS, and higher DN rates were induced at lower sludge age/increased sludge removal regime. Improved control and optimization of reactor DN-activity may be achieved by further modifying reactor design and management scheme as indicated by the variation in and between the two DN-reactors.  相似文献   

15.
In vivo digestibility determination in shrimp is a challenge because these animals are coprophagous, benthic and slow feeders and the small amount of feces that they produce is difficult to collect. The objective of this study was to evaluate an efficient tank design for the purpose of studying shrimp digestibility. Different tank designs were evaluated considering drain system (dual-drain and single-drain), water inlet flow rate (8, 12, and 16 L min−1) and bottom drain diameter (6, 13, 19, 25 and 50 mm) and their effects on tank hydraulics, water velocity and solids flushing. A circular and slightly conical 500 L tank was adapted with a clarifier for the two dual-drain designs (Cornell-type and central-type) and settling columns for the two single-drain designs (Guelph-F and Guelph-L). Results showed that: (1) water rotational velocity profile was more homogeneous in tanks with larger bottom drain outlets, and water velocity increased with water inlet flow rate from almost zero up to 14.5 ± 0.7 cm s−1; (2) solids flushing, measured as the percentage of feed pellets retained at both the bottom drain and in the settling devices, was positively correlated with the surface loading rate (L min−1 flow per m2) and was more effective at the Guelph-L design fitted with a 150 mm diameter settling column. In this system 100% of the solids were removed at the inflow rate of 16 L min−1. It can be concluded that among the systems evaluated, the Guelph-L at an inflow-rate of 12 L min−1 was most efficient for both solids removal and water velocity profile and thus seemed more suitable for shrimp digestibility studies in high performance conditions. Technologies involving hydrodynamic must be intensively applied to solids removal for aquatic species production as well as research purposes like digestibility, which is highlighted in this study.  相似文献   

16.
《Aquacultural Engineering》2010,42(3):166-175
Fish oxygen requirement is a fundamental variable of aquaculture system design and management, as it is the basis for determining water flow rates for sustaining stock. A study on oxygen consumption of California halibut (Paralichthys californicus) between 3.2 and 165.6 g was conducted in small raceways (2.41 m long, 0.28 m wide, and 0.22 m high; operational water depth between 0.05 and 0.10 m with a quiescent zone 19 cm long in the effluent section) working as open respirometers in a recirculating system under farm-like conditions. The fish were fed commercial dry pelleted feeds at a ratio of ∼0.70–3.00% of body weight (BW) and stocked at densities between 94% and 316% percent coverage area (PCA). Oxygen consumption rates were determined by mass balance calculations. The mean and maximum oxygen consumption rates (g O2/kg fish/day) for juvenile California halibut under the conditions tested can be expressed by Mday = 15.077W−0.2452 and Mday = 17.266W−0.2033, respectively, where W is fish weight in grams. The determination of oxygen consumption by California halibut in farm-like conditions provides valuable information on the oxygen requirement of these fish in an aquacultural setting. This information can be used for designing and sizing a rearing facility for the intensive culture of California halibut.  相似文献   

17.
Anaerobic digestion is a way to utilize the potential energy contained in solid waste produced in recirculating aquaculture systems (RASs), either by providing acidogenic products for driving heterotrophic denitrification on site or by directly producing combustive methane. In this study the biochemical acidogenic potential of solid waste from juvenile rainbow trout was evaluated by measuring the yield of volatile fatty acids (VFA) during anaerobic digestion by batch or fed-batch reactor operation at hydrolysis time (HT)/hydraulic retention time (HRT) of 1, 5, or 10 days (and for batch additional 14 and 20 days) in continuously stirred tank reactors. Generally, the VFA yield increased with time and no effect of the reactor type used was found within the time frame of the experiment. At 10 days HT or 10 days HRT the VFA yield reached 222.3 ± 30.5 and 203.4 ± 11.2 mg VFA g−1 TVS0 (total volatile solids at day 0) in batch and fed-batch reactor, respectively. For the fed-batch reactor, increasing HRT from 5 to 10 days gained no significant additional VFA yield. Prolonging the batch reactor experiment to 20 days increased VFA production further (273.9 ± 1.6 mg VFA g−1 TVS0, n = 2). After 10 days HT/HRT, 16.8–23.5% of total Kjeldahl N was found as TAN and 44.3–53.0% of total P was found as ortho-phosphate. A significant difference between reactor types was detected for the phosphorous dissolution at 5 days HT/HRT as a relatively steep increase (of a factor 2–3) in ortho-P content occurred in fed-batch reactors but similar steep increase was only notable after 10 days HT for batch reactors. No differences between reactor types at the other HT/HRT were recorded for P as well as (for all HT/HRT for) N. Based on this study a HRT of approximately 5 days would be recommended for the design of an acidogenic continuously stirred reactor tank in a RAS single-sludge denitrification set-up. The biochemical methane potential of the sludge was estimated to 318 ± 29 g CH4 g−1 TVS0 by a batch assay and represented a higher utility of the solid waste when comparing the methane yield with the VFA yield (in COD units). This points toward a technological challenge of ultimately increase the acidogenic output to match the methane yield as both products are formed from the same source.  相似文献   

18.
Potassium permanganate is a chemical compound widely used in aquaculture for the control and removal of parasites, and in the prevention of diseases caused by bacteria and fungi. However, this compound can be toxic to fish, being a strong oxidant. Moreover, there is no consistent information in the literature about its toxicity to non-target organisms. The purpose of this study was to evaluate the acute toxicity (LC50;96h) of potassium permanganate for tilapia, Oreochromis niloticus, and to determine its toxic effects on non-target organisms using ecotoxicological assays performed with the microcrustacean Ceriodaphnia dubia and with the green microalgae Pseudokirchneriella subcapitata. The results showed that the concentration of 1.81 mg L? 1 of potassium permanganate caused acute toxic effect in tilapia fingerlings. The ecotoxicological assays demonstrated that concentrations above 0.12 mg L? 1 can cause chronic toxic effects on non-target organisms, indicating possible deleterious effects on the food chain of the aquatic ecosystem that may receive the discharge of effluents released by fish cultures treated with this chemotherapy. All toxic concentrations determined in this study were below those recommended in the literature for the use of this chemotherapy in fish cultures, demonstrating that this type of therapy should be more carefully considered in order to avoid damage to the treated fish and to the environment.  相似文献   

19.
Scallop larval production systems in Norway have changed from the use of batch to continuous flow through systems (FTS) during the last decade. Energy use to heat water in both larval and spat nurseries is considerable. Two experiments (June 2010 and February 2011) using water recirculation technology (RAS) were performed in large scale systems (3500 L larval tanks) supplied with continuous addition of algal feed, and 20% renewal of seawater.In the RAS a gradual increase in CO2, decrease in pH and dissolved oxygen was observed over time. This was most obvious during experiment two, when the total organic carbon content increased in both FTS and RAS. The total bacterial number was lower and more stable in FTS than in the RAS. The variations in seawater quality parameters were smaller during the first experiment compared to the second, when values of oxygen saturation were reduced to <70%, pH was 7.8 and NO3− reached 5 mg L−1. Even though these changes would seem less beneficial for survival and growth of scallop larvae, results showed that the survival at the end of the larval stage was higher in the FTS, but the yield of competent larvae ready for settlement was not significant different (p > 0.05) due to large variations between tanks. The CV% was 28.9% in FTS, while it was 49.9% in RAS. In FTS the mean yield was 40.2%, while it was 26.5% of initial number of larvae in RAS. Large variations in survival and yield were found between the larval tanks as well as gradual reduction in pH and oxygen in RAS tanks. The results indicate that there is a large potential for 80% reduction in water use by utilizing recirculation technology.  相似文献   

20.
Fish health under live haul transportation on wellboats and in other recirculating aquaculture systems depends on frequent and reliable measurements of water quality, that may change in response to changes in the environmental conditions and treatment processes. While reliable technologies exist for sensors measuring some water quality parameters such as Oxygen concentration and salinity, there is a lack of sensor technologies for the measurement of other critical water quality parameters such as water pCO2 and NH3 concentrations. Presented is the theory of operation and performance of prototype optical sensors for the measurement of pCO2 and NH3, as well as the methods used for their calibration and characterization. In order to evaluate the sensor’s suitability for aquaculture applications we temporarily installed the sensors on a wellboat and monitored the water quality during the transportation of live mature Atlantic salmon between fish farms and slaughter facilities on the Norwegian coast. Under transportation with different stocking weights and recirculation conditions, the CO2 optode prototypes recorded measurements that coincided with measurements from standard laboratory analysis of spot samples. The pCO2 concentration in the well throughout the testing was shown to vary between approximately 300 μatm and 20 000 μatm. Compared to the pH derived pCO2 estimation method widely applied in aquaculture, the CO2 optode was more sensitive to small fluctuations in CO2 concentration, and gave measurements closer to the CO2 values recorded by laboratory analysis of spot samples. The NH3 optode reported measurements that were consistent with spot samples analyzed using the salicylate–hypochlorite reaction. In contrast to pCO2, the concentration of NH3 during the observed wellboat missions was found to be very low and stable at 0.8 ± 0.3 μg L−1. Once fully developed, the CO2 and NH3 optodes could contribute to better water quality control and efficiency during well boat transportations and other recirculating aquaculture systems.  相似文献   

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